Spacecraft thermal control is an important issue for the design and operation of a spacecraft. The deployment cost of a spacecraft depends significantly on the spacecraft weight and volume. Volume of a spacecraft depends largely on the amount of heat that needs to be dissipated by the available surface area of the spacecraft. Increasing the amount of heat that needs to be dissipated increases the spacecraft surface area needed for heat rejection. An increase in spacecraft surface area translates into increased spacecraft perimeter area and volume even though the volume may not be efficiently used. Increased spacecraft volume leads to increased spacecraft costs.
Spacecraft thermal loading occurs due to equipment dissipation and external loads from the earth and sun. Prior art thermal control systems rely on passive thermal control to relieve spacecraft thermal loads. One such system uses surface radiators which must be located on an external surface of the spacecraft. This greatly reduces the amount of prime external surface area available for payload components requiring external surface mounting. Another passive thermal control system uses a deployable heat pipe system for dissipating thermal loads. This system can only dissipate thermal loads through radiation and requires a deployment mechanism which adds weight and complexity to the spacecraft.
For conventional passive thermal control systems, a surface's ability to reject heat to space and maintain temperatures below some limit is determined by the worst case external load on that surface. This means that excess surface area is required to handle maximum thermal loads which may exist only for a short time or during a specific season.
Spacecraft battery life often determines the useful life of a spacecraft. One of the most frequent causes for spacecraft battery failure is thermal cycling. For this reason, conventional spacecraft typically have batteries located adjacent to external panels of the spacecraft on zenith or north/south surfaces and the batteries are thermally controlled with separate thermal blankets, radiators, and heaters to thermally isolate the batteries from the remainder of the spacecraft. This not only consumes prime external panel area but also unnecessarily increases spacecraft weight.
Spacecraft thermal control systems also include heaters for various components. In order to maintain thermal balance of payload components, replacement heaters are turned on when payload power is off. In addition thermostatic controlled heaters are placed on various propulsion system valves and other components to prevent temperatures from getting too cold.
Thus, the issue of thermal control of a spacecraft has not been completely resolved. Conventional thermal control systems increase spacecraft weight and require an undesirably large amount of prime external surface area for heat dissipation. Moreover, conventional systems use electrical heaters to heat various components thus reducing the amount of available electrical power to operate payload components.